Higher Collapse Pressure Research Articles

Research on cavity collapse characteristics during high-speed water-exit of the supercavitating projectile

During high-speed water-exit of the supercavitating projectile, the cavity interacts with the free surface and collapses, with instantaneous high collapse pressure impacting on the projectile. In order to study the cavity collapse characteristics during high-speed water-exit of the supercavitating projectile, the numerical study based on the Reynolds-averaged equation and the volume of fluid multiphase flow model is conducted in this paper. The results show that the cavity near the free surface will gradually become larger with the movement of the projectile during water-exit of the supercavitating projectile. The existence of attitude angles will cause the asymmetry of cavity to collapse. The cavity on the upstream side will first collapse and generate collapse pressure, while the cavity on the downstream side will collapse later but generate higher collapse pressure. The asymmetry of the cavity collapse becomes stronger with the increasing attitude angles. The time interval of the collapse pressure on the downstream and upstream sides of the projectile becomes shorter close to the projectile tail.

Photophysical and morphological properties of Langmuir–Blodgett films of benzothiadiazole derivatives

Organic semiconductors with extended π-conjugate systems have been extensively investigated to be implemented and improve optoelectronic devices. It is well known that benzothiadiazole (BTD) derivatives have interesting semiconductor properties that make them suitable materials for optoelectronic applications. In this work, the photophysical properties of 4 BTD with triphenylmethyl and triphenylsilyl derivatives in solution exhibited larger Stokes shifts, which can be attributed to the length and conjugation of these molecules. On the other hand, the quantum yields observed for these systems were larger than 0.5. In addition, the formation of Langmuir monolayers at the air–water interface with isotherms showing high collapse pressures around 60 mN/m, and stable compression–decompression cycles (hysteresis) were obtained. Langmuir–Blodgett films onto glass substrates were formed with these compounds by using the Z-type deposit with transfer ratios close to 1. In addition, high-fluorescence emission responses were observed for the BTD derivatives that did not contain silicon in their structure. Also, using scanning electron and atomic force microscopies, regular surface morphologies were observed for the silicon-less compounds, but higher roughnesses and fiber-like structures for the other films. From these results, these BTD films can be potential candidates to be employed in photoelectronic applications.

Cellulose Nanofiber Nanosheet Multilayers by the Langmuir–Blodgett Technique

We describe a systematic approach for producing cellulose nanofiber (CNF) nanosheets using the Langmuir-Blodgett (LB) technique. The CNFs were obtained from sulfuric acid hydrolysis of commercially available microfibrillated cellulose. Needle-like CNFs, negatively charged by grafted sulfate groups, were maintained at the air-water interface, assisted by amphiphilic polymer, poly( N-dodecyl acrylamide) (pDDA). The CNFs produced a stable monolayer. The surface pressure increased steadily with a high collapse pressure of 50 mN m-1 when spread with formic acid and pDDA. The composite monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. Upstroke and downstroke transfer ratios of the films were, respectively, unity and 0.88, indicating that full coverage was achieved by the monolayer even for more than 200 layers. Results obtained using atomic force microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy showed that CNF nanosheets possess well-defined layer structures with average monolayer thickness of 5.3 nm. The relative amount of CNFs in the nanosheets was calculated as 62.6 wt % using the quartz crystal microbalance technique. The as-prepared nanosheets are optically transparent to visible light and have high hydrophobicity. In fact, the nanosheet transparency was higher than 88% at 600 nm wavelength for 24 layers. A miniscule amount of pDDA enables demonstration of free-standing CNF nanosheets with 1 cm width and 45.6 nm thickness (23 layers).

Two-Dimensional Proton Conduction in Biomimetic Polymer Electrolytes Prepared the Polymer Nanosheet Multilayer Film

1．Introduction Organic materials which efficiently transport protons are used in various energy harvesting such as fuel cells and ATP production. Recently, it has been reported that proton transport in the organic materials can be controlled by electric field. [1] In general, protons are transported in two dimension in the protonic transistor, which suggest the importance of fabricating two dimensional proton conductive channel. Biological membrane is a good example for such two dimensional proton conduction. Thus we mimicked the proton conduction at the biological membrane by using polymer nanosheet multilayer film. [2] [3] In this study, we introduce amphoteric group, phosphonic acid to the polymer nanosheet multilayer film. The proton conductivity through the interlayer of the multilayer film was studied by impedance spectroscopy and the mechanism of two dimensional conduction was proposed. 2．Experiment N-dodecylacryamide-co-phosphonic acid copolymers, [p(DDA/VPA)] (Fig. 1) were synthesized by free radical copolymerization of DDA with VPA in ethanol. The monolayer properties of p(DDA/VPA) were investigated by π−A isotherm measurements. The polymer was depositioned on a substrate using the Langmuir-Blodgett (LB) method and film was characterized by X-ray diffraction (XRD) measurement. p(DDA/VPA) was deposited on the substrate with comb-type Au electrode to study the proton conductivity by impedance measurements. 3．Result and discussion The syntheses of p(DDA/VPA) copolymer were confirmed from 1H-NMR and FT-IR. The mole fractions of VPA in the copolymers (n) were determined to be 0.19〜0.52, by elemental analysis. π-A isotherms in all copolymers showed a steep rise in surface pressure and relatively high collapse pressure, indicating that the copolymers formed a densely packed polymer monolayer. The average limiting surface area of VPA suggested that the VPA units were located below the water surface. The lamellar structure of the nanosheet multilayer film prepared using the LB was confirmed by X-ray diffraction measurement. Because the interlayer space increased with n, p(DDA/VPA) formed a multilayer in which a phosphonic acid group is sandwiched between hydrophilic sites (Fig. 2). The proton conductivity parallel to the lamellar plane direction increased with VPA content until n = 0.41 and became 2.6 × 10-2 S cm-1 at 60 ˚C and 98% RH(Fig. 3). Interestingly, the conductivity of n = 0.45 decreased to 1.0×10-2 S cm-1 nevertheless the number of proton source was increased. From the result, we suggest that there is an optimal distance of acid group to achieve a high proton conduction in two dimensional nanospaces. [4] 5．Acknowledgments This work was supported by the Research Program “Dynamic Alliance for Open Innovation Bridging Human, Environment and Materials” within the “Network Joint Research Center for Materials and Devices”. 6．References [1] C. Zhong, et al. Nat. Comm, 2011, 2, 476. [2] T. Sato et al., Langmuir, 2017, 33 (45), 12897–12902. [3] T. Sato et al., Langmuir, 2015, 31 (18), 5174–5180. [4] V. B. P. Leite et al., Phys. Rev. E, 1998, 57, 6835-6839 Figure 1

Hybrid film formation of a water-insoluble quaternary alkylammonium cation with clay-mineral-layers

A solution of the water-insoluble quaternary alkylammonium salt with the long hydrocarbon chain, CH3(CH2)29N(CH3)3·I (C30TMA+·I−), was spread on water and clay mineral (montmorillonite) dispersion surfaces to investigate film formation behavior of the amphiphilic ammonium cation by π-A isotherm curve measurements, AFM observation, IR spectroscopy, and XRD measurements. The C30TMA+ cations formed a stable Langmuir film on the water surface. The Langmuir films were deposited on a substrate to fabricate the multilayer, in which the cations stood nearly perpendicularly to the substrate with the all-trans conformation and they were packed closely with two-dimensional ordering. The negatively charged clay-mineral-layers were adsorbed on a floating Langmuir film of the cation at an air-clay mineral dispersion interface. On the dilute clay mineral dispersion surface, some parts of the floating film of the cation were adsorbed by the clay-mineral-layers and the C30TMA+ cations stood on the clay-mineral-layers. As the clay mineral concentration in the dispersion increased, the π-A isotherm curve for the C30TMA+ cation at the air-dispersion interface shifted to the larger molecular area side with high collapse pressures (40–50mNm−1). Almost whole area of the floating film was covered with the clay-mineral-layers on the concentrated dispersion surface, and the cations stood nearly perpendicularly on the clay-mineral-layers.

Numerical 3D flow simulation of ultrasonic horns with attached cavitation structures and assessment of flow aggressiveness and cavitation erosion sensitive wall zones

As a contribution to a better understanding of cavitation erosion mechanisms, a compressible inviscid finite volume flow solver with barotropic homogeneous liquid–vapor mixture cavitation model is applied to ultrasonic horn set-ups with and without stationary specimen, that exhibit attached cavitation at the horn tip. Void collapses and shock waves, which are closely related to cavitation erosion, are resolved. The computational results are compared to hydrophone, shadowgraphy and erosion test data. At the horn tip, vapor volume and topology, subharmonic oscillation frequency as well as the amplitude of propagating pressure waves are in good agreement with experimental data. For the evaluation of flow aggressiveness and the assessment of erosion sensitive wall zones, statistical analyses of wall loads and of the multiplicity of distinct collapses in wall-adjacent flow regions are applied to the horn tip and the stationary specimen. An a posteriori projection of load collectives, i.e. cumulative collapse rate vs. collapse pressure, onto a reference grid eliminates the grid dependency effectively for attached cavitation at the horn tip, whereas a significant grid dependency remains at the stationary specimen. The load collectives show an exponential decrease towards higher collapse pressures. Erosion sensitive wall zones are well predicted for both, horn tip and stationary specimen, and load profiles are in good qualitative agreement with measured topography profiles of eroded duplex stainless steel samples after long-term runs. For the considered amplitude and gap width according to ASTM G32-10 standard, the analysis of load collectives reveals that the distinctive erosive ring shape at the horn tip can be attributed to frequent breakdown and re-development of a small portion of the tip-attached cavity. This partial breakdown of the attached cavity repeats at each driving cycle and is associated with relatively moderate collapse peak pressures, whereas the stationary specimen is rather unfrequently stressed at the end of each subharmonic oscillation cycle by the violent collapse of the complete cavity.

Preliminary Clinical Results and Mechanical Behavior of a New Double-Layer Carotid Stent

Purpose: To evaluate the in vitro mechanical and clinical implant behavior of a next-generation double-layer stent designed for the carotid artery. Methods: The new double-layer CASPER-RX stent was implanted in 12 patients (median age 69 years; 8 men) with high-grade symptomatic internal carotid artery stenoses (mean 82%). In the in vitro experiments, the CASPER-RX stent (8-×40-mm model) was investigated with respect to its radial force on expansion and the bending stiffness of the stent system and of the stent in its expanded state, as well as the collapse pressure in a thin, flexible sleeve. The wall adaptation of the expanded stents was assessed by fluoroscopy after release in a step and curve model. Results: Technical success was achieved in all patients without complications; there was no peri- or postinterventional stroke and no stroke or restenosis after 6 months. In the experimental studies, the bending stiffness of the stent on the delivery system (154.9 N mm2) was significantly lower than when expanded in a 7-mm flexible tube (467.4 N mm2). The radial force on expansion of the stent to 7 mm was low (0.011 N/mm). The collapse pressure was relatively high (0.56 bar) as a result of the stent’s particular stent structure. The stent exhibited significant foreshortening of 27.6%. The conformability to the wall in the step model was relatively smooth; in the curve model, straightening occurred with consecutive slight stenosis. Conclusion: The first clinical results showed a safe implantation behavior without the occurrence of any ischemia. The structure of the new CASPER-RX stent creates an acceptable flexibility, low radial force, and high collapse pressure. The large foreshortening during implantation should be considered as well as the higher bending stiffness, especially when used in elongated carotid arteries.

Localized Tissue Surrogate Deformation due to Controlled Single Bubble Cavitation

Cavitation-induced shock wave, as might occur in the head during exposure to blast waves, was investigated as a possible damage mechanism for soft brain tissues. A novel experimental technique was developed to visualize and control single bubble cavitation and its collapse, and the influence of this process on a nearby tissue surrogate was investigated. The experiment utilized a Hopkinson pressure bar system which transmits a simulated blast pressure wave (with over-pressure and under-pressure components) to a fluid-filled test chamber implanted with a seed gas bubble. Growth and collapse of this bubble was recorded during passage of the blast wave with a high speed camera. To investigate the potential for cavitation damage to a tissue surrogate, local changes in strain were measured in hydrogel slices placed in various configurations next to the bubble. The strain measurements were made using digital image correlation (DIC) technique by monitoring the motion of material points on the tissue surrogate. In one configuration, bubble contact dynamics resulted in compression contact (>60 μs) followed by inertially-driven tension (>140 μs). In another configuration, the influence of local shock waves emanating from collapsed bubbles was captured. Large compressive strains (0.25 to 0.5) that were highly localized (0.18 mm2) were measured over a short time period (<24 μs) after bubble collapse. High bubble collapse pressures 29 to 125 times that of peak blast overpressure are predicted to be the source of these large strains. Consistent with theoretical predictions, these cavitation-based strains are far larger than the strains imposed by passage of the simulated blast wave alone. Finally, the value of this experimental platform to investigate the single bubble cavitation-induced damage in a biological tissue is illustrated with an example test on rat brain slices.

Synthesis of Sulfated Cyclodextrin Amphiphiles with Liposomal Encapsulation Properties

A novel class of amphiphiles with sulfate groups at the C-6 position and palmitoyl groups at the C-2, 3 positions of α-, β-, and γ-cyclodextrin (CD) were efficiently synthesized. These compounds formed stable monolayers with high collapse pressures at the air-water interface. The mixed monolayer behaviors of the 6-O-sulfated CD amphiphiles (SO3-CDC16) in the presence of dipalmitoyl phosphatidylcholine (DPPC) and cholesterol were discussed using the surface pressure-molecular area (π-A) isotherms. The collapse pressures showed maxima at molar ratios of SO3-CDC16 lower than 10 mol%. A morphological analysis of the liposomes containing DPPC and 4 mol% SO3-CDC16 formed in PBS was carried out using transmission electron microscopy with negative staining, and vesicles with maximum diameters of 350-500 nm were observed. Moreover, the releasing ability of these liposomes was examined using a fluorescent compound, calcein. It was clearly shown that liposomes containing SO3-CDC16 could release encapsulated calcein more easily than liposomes consisting only of DPPC, and that the release rate depended on the phase transition temperature of the SO3-CDC16 included in the liposome membrane.

Nano-Level Surface Processing of Fine Particles by Cavitation to Improve the Photocatalytic Properties of Titanium Oxide

Titanium oxide is known as a photocatalytic material that promotes the generation of hydrogen and oxygen from water by sunlight irradiation. In the present study, titanium oxide particles were treated by water jet cavitation generated using an ejector nozzle. Sub-stream suction occurs in small-sized high-pressure ejector nozzles because of the dynamic high pressure. The water containing titanium oxide powder or a mixed powder of titanium oxide and platinum enters the high-pressure water flow as a sub-stream. In the ejector nozzle, generation, growth, and collapse of cavitation are repeated with the particles of titanium oxide and platinum. Because the cavitation has an extremely high collapse pressure, the surface of the titanium oxide particles is processed by the microjets of cavitation in a so-called reactor comprising the ejector nozzle. The titanium oxide particles subjected to ejector cavitation (EC) processing were investigated for improvements to their photocatalytic properties under ultraviolet irradiation. It was found that noted that nano-level roughness is formed by EC processing. The TiO2 particles or TiO2 particles supported by Pt particles as a cocatalyst containing water were introduced into a vacuum chamber and the gases such as hydrogen and oxygen from the particle surfaces were measured by quadrupole mass spectrometry under ultraviolet irradiation. The EC processing was found to increase the amount of gases generated, including hydrogen and oxygen. Moreover, the amount of hydrogen in particular increases remarkably when both EC processing and support of platinum as a co-catalyst are used. It was also found that the titanium TiO2 particles were supporting minute platinum particles that detached from the original Pt particles during EC processing.

Lamellar versus compact self-assembly of lipoguanosine derivatives in thin surface films

We performed a comparative study on the self-assembling properties of four guanosine derivatives with one and two lipophilic chains of two different lengths at the air–water interface and after Langmuir–Blodgett (LB) deposition onto various solid supports (mica, silicon wafer, graphite). At the air–water interface the derivatives with one lipophilic chain exhibit surface compression behaviour with a profound first order phase transition from the liquid-expanded to the liquid-condensed phase. They assemble into lamellar surface formations, whose structural characteristics remain practically unmodified after their transfer onto the solid substrates. Domain regions with orientationally aligned lamellar formations of sizes up to 150μm2 can be obtained. The compression behaviour of double-chain derivatives is more diverse. While the derivative with two decanoyl chains exhibits the liquid-expanded as well as the liquid-condensed phase, the derivative with two hexadecanoyl chains reveals only the condensed-analogous phase with a relatively high collapse pressure. LB films of double chain derivatives show formation of very homogeneous and compact surface structures with high surface coverage.

Novel Bioresorbable Stent Design and Fabrication: Congenital Heart Disease Applications

The design and development of bioresorbable stents tailored for treatment of pediatric patients with congenital heart disease is described. First, we examined the mechanical properties of thermally annealed PL-32 and PL-18 PLLA fibers using an Instron 5565 tensiometer. Stent designs ranging from 3 to 6 mm diameter and up to 15 mm length were examined. We adapted a winding jig to enable fabrication of coiled stents consisting of double-opposed helices. Double-opposed helical stents were thermally annealed for strength and flexibility. Following winding, stents were crimped on appropriately sized balloon catheters, and then expanded in a 37 °C water bath. Mechanical characteristics were measured as a function of stent size and design. PL-32 fiber has stronger mechanical properties with a 33% increase in stiffness. The opposing coil design improves stent expansion for larger stent designs. In addition, the stiffness of small diameter double-opposed helical stents was higher than values for the larger diameter stents hence having higher collapse pressure 1.07 ± 0.02 atm and the resistance to external pressure-induced collapse for larger diameter stents was lower decreasing to 0.63 ± 0.02 atm. The larger deformations at larger diameters were experienced since mechanical strain in the stent fibers is increased under these conditions. This led to increased twisting of the coils and higher striation angle measurements ranging from 17.5° to 26.7° from smaller to larger stents. The large diameter double opposed helix stents showed larger axial shortening of 3–3.5% and higher elastic recoil increase of 1.12%. The PL-32 stents also showed a slower degradation of 5% over 6 months. Modulating the number of coils within the double helical stent design and winding in opposing directions favorably affects stent mechanical properties.

Calculating Method of Wellbore Collapse Pressure Drilling in Fractured Shale Formation

In order to reduce the oil and gas drilling risk and cost, the calculating method of collapse pressure was established to prevent borehole collapse in fractured shale formation. The method was coupled with borehole concentrated stress, induced stress by crack opened and pore pressure change. The influence law of borehole trajectory and crack occurrence was researched. The results show that, collapse pressure increases substantially in small dip fractured shale formation when the well deviation angle exceeds the critical value, and the increase speed is fastest in the direction of maximum horizontal principle stress; collapse pressure is lower when crack is nearly vertical and the tendency parallel to wellbore azimuth for the horizontal well, but when crack dip exceeds 30° and the tendency is not parallel to wellbore azimuth, it is more dangerous for drilling due to the higher collapse pressure. The research results can be used to solve wellbore instability problems and improve drilling efficiency in the similar regions.

Electronic and interfacial behavior of gemini metallosurfactants with copper(ii)/pseudohalide cascade cores

In this paper we discuss the newly synthesized binuclear species [Cu2(L(PY18))2(μ1,1-N3)2(N3)2] (1) and [Cu2(L(PY18))2(μ1,3-SCN)2(NCS)2] (2), as obtained from the monometallic precursor [Cu(L(PY18))Br2]. These gemini metallosurfactants incorporate metal/anion cascade cores and are investigated by experimental and theoretical methods. Diagnostic IR stretches support the presence of μ1,1-bridged (end-on, 2075 cm(-1)) azide groups in 1 and μ1,3-bridged (end-to-end, 2117 cm(-1)) thiocyanate groups in 2. Anion-to-copper LMCT electronic processes at 390 and 440 nm for 1 and at 415 nm for 2 reinforce the nature of the metal/anion cascade cores. Both species are redox-active, magnetically uncoupled due to poor orbital overlap, and robust in the presence of strongly coordinating solvents. At the air-water interface, 1 and 2 yield Langmuir films with high collapse pressures of ca. 60 mN m(-1). Domain formation is considerably less extensive than that observed for the related monometallic precursor and the average molecular areas are in good agreement with their modeled molecular size. The resulting Langmuir-Blodgett films are isolated on silica substrates and investigated using IR-reflectance/absorbance spectroscopy.

Pressure-Induced Collapse in Double-Walled Carbon Nanotubes: Chemical and Mechanical Screening Effects

The vibrational properties of double-walled carbon nanotubes (DWNTs) is investigated by high-pressure resonance Raman scattering up to 30 GPa in two different pressure-transmitting media (PTM): paraffin oil and NaCl. The protection effect on the outer tube during compression is verified .The collapse of DWNTs is experimentally observed for the first time, showing to be two-step: the onset of the outer 1.56 nm diameter tube collapse at ∼21 GPa is followed by the collapse of the inner 0.86 nm diameter tube at a higher pressure of ∼25 GPa. This observation is supported by calculations. We show that filling a tube with another tube leads to a pressure stabilization against collapse, in strong opposition to what is observed when filling a tube with fullerenes or iodine. The collapse pressure in DWNTs appears to follow a 1/dtav3 law, where dtav is the average diameter from the inner and outer tubes, in agreement with predictions [Yang, X.;Appl. Phys. Lett. 2006, 89, 113101]. Contrary to SWNTs and peapods, for DWNTs, the observed collapse pressure is independent of the PTM nature. Those differences are discussed in terms of tube filling homogeneity and of the separate roles of inner and outer tubes: the outer tube offers chemical screening to the inner tube, whereas the inner tube guarantees mechanical support to the outer one. This leads to high collapse pressure independent of the DWNT environnment: a characteristic that makes DWNTs ideal fillers for composite nanomaterials for high load mechanical support.

Effect of Liquid Metal Composition and Test Material on Cavitation Erosion

Cavitation erosion tests using a vibratory apparatus were carried out to study the effects of liquid metal composition and test material of different stainless steels and a high chromium steel. The relative temperature was defined as the percentage between freezing and boiling points. At a relative temperature of 14 °C, the erosion rate is 10 to 12 times larger in various lead-bismuth alloys and 2 to 5 times larger in sodium than in deionized water. When SUS304 was exposed to cavitation in PbBi, the surface was work-hardened 20% harder compared with original surface. In deionized water, SUS304 was work-hardened by 5%. Therefore, we can conclude that higher collapse pressure can be estimated to act on the specimen surface in lead-bismuth, as compared with that in water. The erosion rate of stainless steels depends on hardness and Hirayama's Ni equivalent. Erosion resistance is the highest for SUS304 and decreases in the order, 9Cr-1Mo steel, SUS403.

The Numerical Simulation of Collapse Pressure and Boundary of the Cavity Cloud in Venturi

The idea that the collapse proceeds from the outer boundary of the cavity cloud towards its center for the ultrasonic cavitation proposed by Hasson and Morch in 1980s is further developed for calculating the collapse pressure and boundaries of cavity cloud at the collapse stage of bubbles for hydraulic cavitation flow in Venturi in present research. The numerical simulation is carried out based on Gilmore's equations of bubble dynamics, which take account of the compressibility of fluid besides the viscosity and interfacial tension. The collapse of the cavity cloud is considered to proceed layer by layer from the outer cloud towards its inner part. The simulation results indicate that the predicted boundaries of the cavity cloud at the collapse stage agree well with the experimental ones. It is also found that the maximum collapse pressure of the cavity cloud is several times as high as the collapse pressure of outside boundary, and it is located at a point in the axis, where the cavity cloud disappears completely. This means that a cavity cloud has higher collapse pressure or strength than that of a single bubble due to the interactions of the bubbles. The effects of operation and structural parameters on the collapse pressure are also analyzed in detail.

Discotic Mesogen – DNA Complex Films at Interfaces

In this article, we review our studies on discotic mesogen – DNA complex films at interfaces. Discotic molecules are known to form highly anisotropic structures at the air-water (A-W) interface. We have studied films of a novel ionic discotic mesogenic molecule, pyridinium salt tethered with hexaalkoxytriphenylene (PyTp) and its complex with DNA (PyTp-DNA) at A-W and air-solid interfaces. The PyTp monolayer was formed on the aqueous subphase containing small amount of DNA. The electrostatic interaction between PyTp and DNA molecules results in a PyTp-DNA complex monolayer. Compared to the pure PyTp monolayer, the PyTp-DNA complex monolayer exhibits higher collapse pressure and lower limiting area. Surface manometry and Brewster angle microscope studies of the PyTp-DNA complex monolayer film indicate the molecules to be in the edge-on configuration. With increase in surface pressure, the complex monolayer undergoes a transition from a loosely packed monolayer phase to a compactly packed monolayer phase. The PyTp-DNA complex films on silicon wafers were prepared using Langmuir-Blodgett (LB) technique. We find that several tens of layers of PyTp-DNA complex monolayer can be transferred with good efficiency. We have carried out nanoscale electrical conductivity measurements for the pure PyTp and PyTp-DNA complex LB films using current sensing atomic force microscope. We have studied the current-voltage (I-V) characteristics for the metal-LB film-metal junction and our analysis shows that the I-V curves followed the Fowler-Nordheim tunneling model.

Molecular Order in Langmuir−Blodgett Monolayers of Metal−Ligand Surfactants Probed by Sum Frequency Generation

Molecular organization of Langmuir-Blodgett (LB) monolayers of novel copper-containing metal-ligand surfactants was characterized by the surface-selective vibrational sum frequency generation (SFG) spectroscopy. The orientational and conformational order inferred from the SFG peak amplitudes and line shapes were correlated with the two-dimensional phases of the monolayers observed in the compression isotherms. The octadecyl-pyridin-2-ylmethyl-amine (L(PyC18)) ligand by itself shows good amphiphilic properties, as indicated by the high monolayer collapse pressure at the air/water interface, but its LB films transferred onto fused silica exhibit a high degree of trans-gauche conformational disorder in the alkyl tails. Coordination of copper(II) ions to the chelating head group enhances the molecular alignment and reduces the fraction of gauche defects of the alkyl chains. Monolayers of single-tail (L(PyC18)Cu(II)Cl(2)) and double-tail [(L(PyC18))(2)Cu(II)]Cl(2) metallosurfactants show distinctly different behavior of their molecular organization as a function of the area per molecule. Our observations suggest metal-ligand interactions as a pathway to induce molecular order in LB monolayer films.

Mixed DPPC/DPPG Monolayers at Very High Film Compression

A drop shape technique using a constrained sessile drop constellation (ADSA-CSD) has been introduced as a superior technique for studying spread films specially at high collapse pressures [Saad et al. Langmuir 2008, 24, 10843-10850]. It has been shown that ADSA-CSD has certain advantages including the need only for small quantities of liquid and insoluble surfactants, the ability to measure very low surface tension values, easier deposition procedure, and leak-proof design. Here, this technique was applied to investigate mixed DPPC/DPPG monolayers to characterize the role of such molecules in maintaining stable film properties and surface activity of lung surfactant preparations. Results of compression isotherms were obtained for different DPPC/DPPG mixture ratios: 90/10, 80/20, 70/30, 60/40, and 50/50 in addition to pure DPPC and pure DPPG at room temperature of 24 degrees C. The ultimate collapse pressure of DPPC/DPPG mixtures was found to be 70.5 mJ/m2 (similar to pure DPPC) for the cases of low DPPG content (up to 20%). Increasing the DPPG content in the mixture (up to 40%) caused a slight decrease in the ultimate collapse pressure. However, further increase of DPPG in the mixture (50% or more) caused a sharp decrease in the ultimate collapse pressure to a value of 59.9 mJ/m2 (similar to pure DPPG). The change in film elasticity was also tracked for the range of mixture ratios studied. The physical reasons for such changes and the interaction between DPPC and DPPG molecules are discussed. The results also show a change in the film hysteresis upon successive compression and expansion cycles for different mixture ratios.